Investigations are being conducted into aspects of specialization of the primate and human retina into the macula, as well as into tissue-tissue interactions which are necessary for the maintenance of a normally functioning retinochoroidal complex. The macula-specific concentrations of various cyclic nucleotides have been investigated by radioimmunoassay in normal and diseased human as well as rhesus monkey retinas, pigmented epithelia, and choroids. By performing controlled experiments with rhesus monkey retinochoroidal tissues, the time course of stability of the stable pool of cyclic nucleotides in these tissues was determined and used as a basis for interpreting the human studies. Certain enzymes such as tyrosinase have also been measured in geographically specific areas of the retinochoroidal complex. The sensitivity of retinal-pigmented epithelial and choroidal cells to immunoglobulin labeled erythrocytes in normal Irish setter pups and those with inherited rod-cone displasia was tested. The specificity of the ingestion of radioactively labeled photoreceptor outer segments was also examined by cell culture techniques using liquid scintilation counting and electron microscopic detection of phagosomes for confirmation.